To obtain an instance of an implementation of the System.Text.Encoder class, the application should use the Encoding.GetEncoder method of an System.Text.Encoding implementation.

The Encoder.GetByteCount(Char*, int, bool) method determines how many bytes result in encoding a set of Unicode characters, and the Encoder.GetBytes(Char*, int, Byte*, int, bool) method performs the actual encoding. There are several versions of both of these methods available in the System.Text.Encoder class. For more information, see Encoding.GetBytes(Char*, int, Byte*, int).

A System.Text.Encoder object maintains state information between successive calls to GetBytes or Decoder.Convert(Byte[], int, int, Char[], int, int, bool, Int32@, Int32@, Boolean@) methods so that it can correctly encode character sequences that span blocks. The System.Text.Encoder also preserves trailing characters at the end of data blocks and uses the trailing characters in the next encoding operation. For example, a data block might end with an unmatched high surrogate, and the matching low surrogate might be in the next data block. Therefore, Encoding.GetDecoder and Encoding.GetEncoder are useful for network transmission and file operations, because those operations often deal with blocks of data instead of a complete data stream.

Version Considerations

A System.Text.Decoder or System.Text.Encoder object can be serialized during a conversion operation. The state of the object is retained if it is deserialized in the same version of the .NET Framework, but lost if it is deserialized in another version.

The following example demonstrates using the System.Text.UTF8Encoding class to convert one character array to two byte arrays.

using System;
using System.Text;

public class EncoderExample
{

   public static void Main()
   {

      string str = "Encoder";
      char[] cAry = str.ToCharArray();
      UTF8Encoding utf = new UTF8Encoding();
    
      Encoder e = utf.GetEncoder();
      int count1 = 
         e.GetByteCount(cAry,0,cAry.Length-4,false);
      int count2 = 
         e.GetByteCount(cAry,cAry.Length-4,4,true);
      byte[] bytes1 = new byte[count1];
      byte[] bytes2 = new byte[count2];
      
      e.GetBytes(cAry,0,cAry.Length-4,bytes1,0,false);
      e.GetBytes(cAry,cAry.Length-4,4,bytes2,0,true);

      Console.Write("Bytes1: ");
      foreach (byte b in bytes1)
         Console.Write(" '{0}' ", b);
      Console.WriteLine();

      Console.Write("Bytes2: ");
      foreach (byte b in bytes2)
         Console.Write(" '{0}' ", b);
      Console.WriteLine();
            
   }

}

The output is